Panel illuminating system



APrl] 1962 cs. K. c. HARDESTY 3,027,668

PANEL ILLUMINATING SYSTEM Original Filed Sept. 50, 1958 I4 I40 I40 |4b 32a 34b 32b 34 36C 32C mNm k A INVENTOR e. K. c. HARDESTY or) J;

United States Patent M 3,027,668 PANEL ILLUMINATING SYSTEM George K. C. Hardesty, Box 156, Mayo, Md.

Original application Sept. 30, 1958, Ser. No. 764,462, now

Patent No. 2,982,039, dated May 2, 1961. Divided and this application Nov. 19, 1959, Ser. No. 854,210

4 Claims. (Cl. 40--130) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This application is a division of application Serial No. 764,462 filed September 30, 1958, now Patent Number 2,982,039.

This invention relates to the illumination of instrument dials, panels, plotting boards and the like, and particularly to the provision of an eflicient and practical panel which is suited for many uses aboard ships, surface or submarine, aircraft and in other installations having large numbers of visual indicators.

More particularly, this invention relates to indirect lighting in combination with electroluminescent sources.

Heretofore, .edge lighting, that is panel illumination wherein one or more light sources are located at the edge of a transparent panel and light rays introduced into,

the panel for transillumination thereof and indirect illumi-,

nation thereby, has beencarried out more or less exclusively by tungsten filament lamps, fluorescent lamps or the like located at the edge of the panel; hence the name edge lighting.

7 Electroluminescence, on the other hand, has been used only for direct viewing. That is, pointers, indicia or the like are either formed as electroluminescent members or are located directly in front of electroluminescent members to be made visible as silhouettes by visual contrast. A fire exit sign, for example might consist of a rectangular electroluminescent lamp and an opaque mesh concealing all of the lamp except the areas in the words Fire Escape. This has obvious inefficiency as most of the energy is lost in the mask.

Electroluminescent light sources have certain inherent advantages over tungsten filament lamps; For example, for panel illumination, 6 volts is a practical maximum that may be used for the miniature lampsrequired. Tungsten filaments arerich in red lightand they emit appreciable light through the several bands of the visible spectrum at this conservative voltage, and such lamps have a relatively long life. However, as tungsten filaments are dimmed, by design, the other bands of the visible spectrum disappear and substantially only red light is emitted. Electroluminescent light sources, on the other hand, operate most efiiciently at around 250 volts. Electroluminescent sources can efliciently emit light rays from orange-yellow through blue, with practically no emission of red rays. The color characteristics of light rays emitted by an electroluminescent source, however, do not appreciably change with dimming.

An object of the present invention is to provide an eificient and practical illuminated panel in the nature of an indirectly illuminated panel in which all areas of the electroluminescent source contribute to the luminance of the panel markings.

A further object of this invention is to provide an illuminated panel utilizing electroluminescent sources for indirect lighting.

The broad principles of this invention may be applied to edge-lighted plotting boards and to see thru trans parent illuminated scales, dials, pointers and the like.

Briefly, this invention facilitates the viewing of nonelectroluminescent indicia and other graphic material 3,027,658 Fatented Apr. 3, 1962 made luminous by light given off by concealed electro luminescent sources applied to suitable hidden surfaces of a transparent, light-conducting panel.

By this invention, the utility of electroluminescent lamps in instrument illumination is greatly extended, since it is not necessary that the electroluminescent material itself be viewed. The indicia or markings, for example, may be of suitable, high diffuse reflectivity, opaque or translucent, materials chosen for excellent daylight visibility as well as high apparent luminosity when viewed at night or in dark environments. The applied indicia may be any color or reflectivity paint, fired on composition, or the like, or the Coming Glass Works type of photosensi tive graphic technique may be used to produce indicia within an edge illuminable glass member.

Although the instant invention may be used with a single panel illumination system such as applicants Patent No. 2,805,505, it is particularly compatible with and may be used with the Duo-Panel System Edge Illumination System, illustrated and described in applicants co-pending application Serial No. 369,976, filed July 23, 1953, now Patent No. 2,886,911.

The invention, together with the above and other ob jects and advantages thereof, is set forth in more technical detail in the following description when considered in connection with the accompanying drawing wherein like reference numerals designate like parts throughout the several views thereof and wherein the sole FIGURE illustrates a duo-panel embodiment indicated generally by the numeral 10. In this figure a light-transmitting panel 12 is fabricated of highly transparent material such as glass or, preferably, an acrylic resin ,or methyl methacry-late plastic, with the front and back surfaces of the panel in parallel relation and polished to provide smooth optical surfaces. The back or reverse surface of the light-transmitting panel is preferably covered throughout its area with a-material having high specular reflectivity. This material, indicated at 30, may be polished-faced metal foil, polished metal sheets, evaporated metal deposited on the surface as a film, or oriented flake metallicpigmented coatings. The front surface of the light-trans:

mitting panel is at least partially covered with an electroluminescent light source, indicated generally at 14. The electroluminescent material of this embodiment includes a transparent'current carrying lamina 14b, an electroluminescent lamina 14a, and an opaque current carrying lamina 140. A pair of leads 14d are connected to conductors 14band 14c and lead to and from a suitable source of AC. current, not shown. The: electroluminescent light source is provided with optionally-placed openings therein for transmission of light therethrough, which openings are indicated at 32a, 32b and 32c.

Mounted in front of the light-transmitting panel is an indicia panel 34. The indicia panel comprises a lower lamina 34a, made of transparent or translucent plastic, as desired, and an upper lamina 34b made of an opaque material. indicia-forming openings 36a, 36b and 360 are cut in the upper or opaque lamina and are in line with the openings 32a, 32b and 320 formed in the electroluminescent light source. With the arrangement of the illustrative figure, light rays from the electroluminescent source are transmitted through the upper surface of the light-transmitting panel and into the panel at various angles for transmission therethrough. Certain of such light rays are reflected by the mirrored surface 30 back through the openings 32a, 32b and 320 in the light source to thereby illuminate the indicia formed by the openings 36a, 36b and 360 in the opaque lamina 34b. Thus, as with the other embodiments, the indicia are indirectly illuminated by an electroluminescent source which itself is not seen. If desired, the indicia may be colored inserts in the openings 36a, 36b and/or 360 and may be in optical light-transmitting panel by the mere'interface relation of such surfaces. Partial advantages may result from the provision of light diflusing characteristics to the surfaces of the light-transmitting panel in those areas that intercept light from the electroluminescent light source.' These diffusing characteristics may be provided by rough ening the surfaces of the light-transmitting panel which are adjacent the electroluminescent light source and by applying a diffusing surface to the opposite or light reflecting surface of the light-transmitting panel. Where optical contact is provided, light can be regarded as originating under the principal surfaces of the light-transmitting panel and roughening is of less utility.

Having thus described the invention, it is to be understood that the foregoing disclosure relates to only preferred embodiments of the invention and that numerous modifications or alterations may be made therein without departing from the spirit and the scope of theinvention as set forth in the appended claims.

What is claimed is:

l. A duo-panel illuminating system comprising a trans parent light-transmitting panel having'parallel front and rearsurfaces arranged for specular reflection of light therebetween, an electroluminescent light source :posi tioned adjacent the front surface of the light-transmitting panel for introducing light rays into such panel forspecular reflection of light therethrough, said electroluminescent light source covering substantially the entire upper surface of the light-transmitting panel and having openings therein at selected areas thereof for transmission .of light from the panel, light reflecting means formed on the rear surface of the light-transmitting panel for reflecting light rays out of such panel and through the openings in the electroluminescent light source, an indicia panel positioned adjacent the front surface ofthe electroluminescent panel in parallel relation thereto, and indicia forming means on said'indicia panel'in line with the openings in the electroluminescent light source for "illumination thereby.

2. A panel illuminating system comprising a transparent light-transmitting panel having parallel front and rear surfaces arranged forspecular reflection of "light therebetween, an electroluminescent light source positioned adjacent the front surface of the light-transmitting panel for. introducing light rays into such panel for specular reflection of light therethrough, said electroluminescent light source covering substantially the entire upper surface of the light-transmitting panel and having openings therein at selected areas thereof for transmission of light from the panel, a metallic light reflecting layer formedover the rear surface of the light-transmitting panel for reflecting light rays out of such panel and throughthe openings 'in the electroluminescent light source, an indicia panel positioned adjacent the front surface of the electroluminescent panel in parallel relation thereto, and indicia forming means on said indicia panel in linewith the 'openings intheelectroluminescent light source for illumination thereby.

*3. An instrument panel illumination system comprising a first panel of transparent light-transmitting material having principal surfaces operative specularly to reflect light rays therebetween, 'an electroluminescent light source metallic light reflecting layer 'on said back surface over adjacent the front surface of the light-transmitting panel for introducing light rays. into such panel forspecular reflection of light therethrough, said electroluminescent light source "covering substantially'the entire upper surface of the light-transmitting panel and having at least one opening therein at a selected area thereof'for transmission of light from the panel, light reflecting means formed on the rear surface of the light-transmittingpanel for reflecting light rays out of said panel and through the open ings in'the electroluminescent light'source.

4. A panel illuminating system comprising a solid-light transmitting panel of transparent material, said panel having parallel front and back faces polished to provide smooth optical surfaces over the entire areas thereof; a

the entire area thereof, an el ectroluminescent light source positioned adjacent the front surface of said paneland covering substantially the entire surface thereof but having openings therein at selected areas for transmission of light from the panel, an indicia'panel positioned in front of said electroluminescent source in parallel relation thereto, and indicia forming means on saidindicia panel in line with the openings in the electroluminescent light source 7 for illumination thereby.

Ma'sh Dec. 29, 1959 m Hp 

